I agree with your definition of toxic FightingEstrangement and would just add lying.
I agree that an apology "can't undo the damage" but it doesn't necessarily justify estrangement. Rhinestone's DH was given this unfortunate advice by a counselor, a trained professional and sought the advice of his wife at the time, the child's mother who was a social worker, a trained professional. No, that doesn't absolve him of all responsibility but it does go some way to explaining why he took the course of action that he did.
Perhaps, without the advice given by the counselor and the support from his wife at the time, a social worker, he wouldn't have considered disciplining his son in that way.
If this is the reason his son's given for their estrangement, for his refusal to have anything whatsoever to do with his father, I wonder how his son would feel if at some time in the future, one of his children has an issue with the way s/he was parented, despite it being recommended by a professional and cuts him out of his/her life?